This application claims the benefit of Korean Application No. 2000-52660 filed Sep. 6, 2000, in the Korean Patent Office, the disclosure of which is incorporated herein by reference
1. Field of the Invention
The present invention relates to a method of converting an m-bit information word into a modulation signal and restoration of the modulation signal, and more particularly, to a method of modulating and demodulating by which the direct current (DC) component of a codeword stream is effectively suppressed in a run length limited (RLL) code. The method is useful in an optical recording/reproduction apparatus which requires high-density recording/reproduction.
2. Description of the Related Art
The quality of an RLL code, which is expressed as (d,k,m,n), is estimated from the recording density and the amount of suppression of its DC component, which are factors for expressing the performance of the code. Here, m denotes the number of data bits (which may also be referred to as the number of source bits or the number of information word bits), n denotes the number of bits of a modulated codeword (which may be referred to as the number of bits of a channel), d denotes the minimum number of 0s which may consecutively exist between 1 and 1 within a codeword, and k denotes the maximum number of 0s which may consecutively exist between 1 and 1 within a codeword. The interval between bits within a codeword is designated by T.
In a modulation method, the recording density can be enhanced by reducing the number (n) of bits of a codeword while fixing d and m. However, an RLL code must satisfy the minimum number (d) and maximum number (k) of 0s capable of consecutively existing between 1 and 1 within a codeword. Where the number of data bits is m while satisfying this (d,k) condition, it is preferable that the number of codewords which satisfy an RLL(d,k) condition be 2m or greater. However, a portion where two codewords are connected must also satisfy the RLL(d,k) condition in order to actually use the RLL code. Where the DC component of a code affects the performance of a system, as in optical disc recording/reproduction apparatuses, a code intended to be used must have a DC suppression capability.
An important reason why a RLL-modulated code stream must suppress DC is to minimize the influence that a reproduction signal has on a servo bandwidth. Hereinafter, a DC suppressing method is referred to as a digital sum value (DSV) adjustment method.
Two DSV adjustment methods which are commonly used are a method by which a code has a DSV control code and a method of inserting a merge bit whenever a DSV is adjusted. An eight to fourteen modulation plus (EFM+) code performs DSV control using a separate code table, and an EFM code or (1,7) code performs DSV control by inserting a merge bit.
A conventional modulation code group, in which a code has a DSV control code for controlling DC suppression while satisfying the above-described condition, includes a predetermined number of main conversion code groups and DC suppression control code groups for performing DC suppression control by pairing with the main conversion code groups. In this case, the codewords within the main conversion code groups are distinguished from each other by several characteristics. That is, the main conversion code groups A and B do not share any codewords which are the same, and if a redundant code is used, there are code groups such as conversion code groups C and D for demodulating the redundant code. Here, the conversion code groups C and D for demodulating a redundant code do not share any codewords which are the same, but the codewords within the main conversion code group A or B may exist in the conversion code group C or D for demodulating a redundant code. The number of codewords in each of the main conversion code groups A and B and the redundant code demodulation conversion code groups C and D is 2m if the number of bits of a non-converted source word is m.
If code groups E through H are DC suppression control code groups capable of controlling DC together with code groups A through D, the codewords within the code groups E through H have the same condition as that of the codewords within the code groups A through D which respectively form pairs with the code groups E through H. That is, in terms of a redundant codeword generation condition or a condition for the number of lead zeros, LZ, of a codeword, the same codeword generation method is applied to the DC suppression control code groups E through H and the code groups A through D that can control DC with the aid of the code groups E through H.
For example, FIG. 2 shows characteristics of an EFM+ code having a run length condition of RLL(2,10) and a codeword length (n) of 16 bits, which is used in current DVDs. There are main conversion code groups MCG1 and MCG2 (groups A and B in FIG. 1, respectively), redundant code demodulation conversion code groups DCG1 and DCG2 (groups C and D, respectively, in FIG. 1), and four DSV code groups (groups E through H in FIG. 1) capable of controlling DC suppression by forming pairs with the conversion code groups. The four conversion code groups and the four DSV code groups for DC control have no identical codewords.
Also, all of the code groups have the same condition for generating a redundant codeword, and the codewords in code group pairs capable of DC control (that is, a pair of MCG1 and a first DSV code group, a pair of MCG2 and a second DSV code group, a pair of DCG1 and a third DSV code group, and a pair of DCG2 and a fourth DSV code group) have the same characteristics.
That is, codewords in each of which the number of 0s continuing from the least significant bit (LSB) of a codeword (which is referred to as the number of end zeros) is 2 to 5 are duplicated. This rule is equally applied to all of the code groups. In each of the codewords within the first DSV code group for controlling DC suppression with the aid of the main conversion code group MCG1, the number of 0s continuing from the most significant bit (MSB) (which is referred to as the number of lead zeros) is 2 to 9. In each of the codewords within the second DSV code group for controlling DC suppression with the aid of the main conversion code group MCG2, the number of lead zeros is 0 to 1. In the codewords within the third DSV code group for controlling DC suppression with the aid of the redundant code demodulation conversion code group DCG1, some bits (here, b15 (MSB) and b3) are xe2x80x9c0bxe2x80x9d. In the codewords within the fourth DSV code group for controlling DC suppression with the aid of the redundant code demodulation conversion code group DCG2, some bits (here, b15 (MSB) or b3) are xe2x80x9c1bxe2x80x9d.
In a conventional modulation method using the modulation code group shown in FIGS. 1 and 2, where the number of codewords to be used to control DC suppression is insufficient, DC suppression control cannot be sufficiently accomplished due to a small number of codewords included within the code groups for controlling DC suppression.
To solve the above problem, an object of the present invention is to provide a run length limited (RLL) code modulating method which is suitable for high-density disc systems, by which the direct current (DC) component of a codeword stream is effectively suppressed.
Another object of the present invention is to provide a modulation method by which the DC component of a codeword stream is effectively suppressed using DC suppression control code groups having codewords having the same properties as the codewords in data modulation code groups which make the most of the sign of parameter CSV representing the DC value of a codeword and of characteristics of parameter INV predicting the DSV transit direction of the next codeword.
Still another object of the present invention is to provide a modulation method by which the probability of controlling DC suppression is increased by relaxing the redundant codeword generation condition and the condition of usable codewords with respect to the codewords in a DC suppression control code group which makes a pair with a data modulation code group.
Yet another object of the present invention is to provide a method of demodulating an RLL code, by which the DC component of a codeword stream is effectively suppressed.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention
To achieve the above and other objects, the present invention provides a method of modulating input data into a run length limited (RLL) code which is expressed as (d,k,m,n), where d denotes a minimum run length, k denotes the maximum run length, m denotes the bit length of data, and n denotes the bit length of a codeword. In this method, m-bit input data is modulated into a codeword, which is favorable for DC suppression, from a predetermined number of first code groups for data modulation and a predetermined number of second code groups for DC suppression control, the first and second code groups having redundant codewords and being produced so that the codewords within the first code group have a first parameter CSV (codeword sum value) which represents the direct current (DC) value of a codeword, the sign of which is opposite to that of corresponding codewords within the second code group, and a second parameter INV which predicts the digital sum value (DSV) transition direction of the next codeword, the characteristic of which is opposite to that of corresponding codewords within the second code group, wherein the first and second code groups have different redundant codeword generation conditions.
To further achieve the above and other objects, the present invention provides a method of demodulating a codeword stream received by an optical recording/reproduction apparatus using a run length limited (RLL) code in which input data has been modulated into a codeword in a code group, which is favorable for DC suppression, from a predetermined number of first code groups for data modulation and a predetermined number of second code groups for DC suppression control, the first and second code groups having duplicate codewords and being produced so that the codewords within the first code group have a first parameter CSV (codeword sum value) which represents the direct current (DC) value of a codeword, the sign of which is opposite to that of corresponding codewords within the second code group, and a second parameter INV which predicts the digital sum value (DSV) transition direction of the next codeword, the characteristic of which is opposite to that of corresponding codewords within the second code group, and the first and second code groups have different duplicate codeword generation conditions. In this method, a codeword stream is received, and a third parameter NCG (next code group) designating a code group having a current codeword to be currently demodulated is updated depending on characteristics of the previous codeword. Next, a determination is made as to whether there are two identical current codewords in a code group designated by the third updated parameter NCG. Then, the current codeword is demodulated into the original data for a codeword in a code group designated by the third updated parameter NCG, if the current codeword does not have a duplicate. Also, the current codeword is demodulated into the original data for one of the two identical codewords selected depending on the LZ of the next codeword, if the current codeword has a duplicate.